The present invention relates to an erecting/lying-down dam or sluice gate made of a flexible sheet.
Erecting/lying-down dams or sluice gates are typically made of a flexible film (for example, rubberized fabric) attached on a riverbed at least in a direction intersecting the river flow with a fluid such as air, water or the like acting as an expanding medium. The medium is discharged from the cover to make the cover lay down through a pumping pipe communicating with the inside of the cover. Such devices are described in Japanese Patent Publication Nos. 40-11702 and 44-2371.
FIG. 1(a) shows such a prior art erecting/lying-down dam or sluice gate made of a flexible film as described above. In the drawing, reference numeral 1 designates a flexible film forming a cover, 2 a foundation of concrete, 3 a watertight sheet forming a base, 4 fittings connecting cover 2 and base 3, 5 air or water inflating the gate, and 6 a stream of water in a river or the like.
Where water exists also at the downstream side, film cover 1 does not completely lay down on foundation 2 when deflating; that is, a floating film F is produced as shown in FIG. 1(c). Of course film 2 does not float if there is no water or little water at the downstream side. FIG. 1(b) shows a midway state where fluid is being discharged.
When the foregoing dam is inflated as an estuary dam, a temporarily shut-up dam, a lock gate, or the like, of course the dam prevents a ship from navigating. However, navigation is not always possible even when the dam is deflated. There is a possibility of damage of a floating film as described above by a ship by its body or screw. Even if the floating film is lying down, there is another possibility of damage by being rolled up by a screw.